U.S. patent application Ser. No. 222,994, filed July 22, 1988 now U.S. Pat. No. 4,858,426 by W. N. Holcomb and assigned to the assignee of this invention, describes a secondary oil system for a flight propulsion gas turbine engine which provides secondary oil flow to a bearing of the engine after interruption of regular or primary oil flow. That system includes an annular reservoir in a sump of the engine surrounding the bearing and a passage from the bottom of the reservoir to a secondary orifice near the bearing. The reservoir is filled from the primary oil system of the engine and continuously drains by gravity through the secondary orifice. The secondary oil system thus operates in parallel with the primary oil system and necessarily commences operation at the instant primary oil flow is interrupted, whether or not secondary oil flow is actually required at that instant. Premature commencement of secondary oil flow may minimize the duration of engine operation after primary oil flow stops. A secondary oil system according to this invention delays the onset of secondary oil flow after primary oil flow stops to maximize the aforesaid duration of engine operation after interruption of primary oil flow.